Method for storing and playing back signals on a carrier

ABSTRACT

In a signal storage system in which signals are stored in the form of spatial undulations in a resiliently compressible surface and played back by compressing the undulation peaks with a substantially motionless pressure responsive transducer, the transducer output having a component whose frequency represents the frequency at which successive undulation peaks are scanned, a second signal is recorded in the form of variations in the ratio of undulation peak length to total undulation length.

O v United States Patent 1 1 3,800,100

Runge A Mar. 26, 1974 METHOD FOR STORING AND PLAYING [56] ReferencesCited BACK SIGNALS ON A CARRIER UNITED STATES PATENTS [75] Inventor:Wilhelm Runge, Ulm/Donau, 3,691,317 9/1972 Dickopp.... 179/100.41 PGermany 3,482,038 12/1969 Warren 178/66 A [73] Assignee: TED BildplattenAktiengesellschaft AEG Telefunken TELDEC g, Primary Examiner Raymond F.Card1llo, Jr. Attorney, Agent, or Fzrm--Spencer & Kaye Switzerland [22]Filed: July 3, 1972 [57] ABSTRACT [21] Appl. No.: 268,553 In a signalstorage system in which signals are stored in the form of spatialundulations in a resiliently compressible surface and played back bycompressing the [30] Foreign Apphcamm Pnonty Dam undulation peaks with asubstantially motionless pres- July 3, 1971 Germany 2133130 Sureresponsive transducer, the transducer output ing a component whosefrequency represents the fre- Eg g 'g 100'4 7% quency at whichsuccessive undulation peaks are W 9 d d d 5' s1 Field ofSearch..179/100.4 R, 100.4 0, a Sewnd s'gnal e m the 179/1004 M, 100.41 P,100.41 13,15 BM; 178/66 A, 6, DIG. 3; 325/139 variations in the ratio ofundulation peak length to total undulation length.

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PR/OF? AR 7 F /G 2 PR/OR ART nmmmmae ism 3800 "100 sum 2 or 3 FIG. 5b

Pmfmwmzs m4 3,800,100

SHEET 3 [IF 3 THRESHOLD GAIN CONTROLLED zggggg g c/Rcu/T AMRL/F/ER'L/M/TER E INTAEGRATORX AMPLIFIER g- I SIC Ya I D CL dI e f T CONTROLLEDTHRESHOLD 5 F c/Rcu/T METHOD FOR STORING AND PLAYING BACK' SIGNALS ON ACARRIER BACKGROUND OF THE INVENTION The signal scanning from thiscarrier is effected by av pickup provided with a mechanical-electricaltransducer responsive to pressure variations. As disclosed in theabove-cited patents, the scanning surface of the pickup remains, duringplayback, substantially motionless in the direction of the force exertedthereon by the surface portions of the carrier, while the surfaceportions are compressed as they pass under the pickup surface and thusexert a pressure force on the pickup surface due to their beingcompressed. The characteristic shape of this pressure force during thepassage of the surface portions under the pickup surface is used by thetransducer to derivean electrical value which corresponds to the storedsignals.

This technique is particularly useful for the storage and playback ofsignals which contain a broadbanded frequency mixture, for exampletelevision picture sig nals.

A number of specific proposals have been made regarding the form inwhich the information is recorded on the carrier. Inter alia, it hasbeen proposed to keep the amplitude of the undulations of the carriersurface tage, for example, when the recorded signal value is a carrieroscillation which is frequency modulated with the signal.

SUMMARY OF THE INVENTION It is an object of the present invention tostore a second information signal on the carrier, simultaneously andwithout any additional space requirement, in addition to the previouslyproposed hill-and-dale frequency modulated information signal, whilemaintaining the frequency-independent amplitude of these undulations onthe carrier surface, and to play the second signal back therefrom. If,for example, the first information signal is the luminance signal of atelevision program, the second information signal may be the chrominancesignal or the'audio signal, possibly also a superimposition of these twosignals.

The present invention thus involves a method for storing and playingback signals on a carrier along a certain track where the signals areconstituted by undulations in mechanically depressable surface portions.During playback the peaks of these undulations, due to their beingcompressed by a pressure sensitive pickup, exert a pressure force on thescanning surface of this pickup. This pressure force is converted intoan electrical ducer.

The objects according to the present invention are achieved by using theundulations, whose number per unit of scanning path length correspondsto the instanvoltage by a mechanical-electrical transtaneous frequencyof a first signal, for the simultaneous storing of a second signal whichis independent of the first signal, and giving each undulation peak sucha length along the scanning path that the ratio between this length andthe total length of the associated undulation period corresponds to therespective characteristic value of the second signal.

The two signals to be recorded are thus stored, according to the presentinvention, by frequency modulation of the first signal and an additionalpulse duration modulation of the second signal.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are idealizedelevational views of a portion of one track of a carrier withhill-and-dale recording for two successive positions of a cooperatingpickup stylus.

FIG. 3 is a curve of the force acting on a pickup during scanning of thecarrier according to FIGS. 1 and FIG. 4 is a curve illustrating thebehavior of the pickup scanning the hill-and-dale recording applied tothe carrier.

FIG. 5a is an idealized cross-sectional view of a carrier with thehill-and-dale recording according to the present invention.

FIG. 5b is a curve of the time sequence of the second informationrecorded on the carrier of FIG. 5a.

FIG. 5c is a pair of curves showing the force produced by the carrier onthe pickup during scanning of the carrier of FIG. 5a.

FIG. 6 is a diagram of a playback arrangement with a filter for use witha carrier produced according to the invention.

FIG. 7 shows a block diagram of the arrangement to produce themodulation signal according to the invention.

arrangement shown in FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 illustrate acarrier 1 provided with groove undulations in the manner described inthe above-cited patents. These figures show a cross section along ascanning track in which the frequency modulated information is recordedaccording to the hill-anddale technique. The recording is in the form ofa train of undulations, with each undulationvbeing composed of aprojection la, 1b, 1c, 1d, 12, 1f, etc., and a space or gap. The lengthof each projection is B and the total length of each undulation,composed of a projection and its succeeding gap, is A. The undulationprojections have a constant height vertical to the scanning direction,and a constant length B. The groove width is constant. The distance Abetween the leading edges of two identical groove undulations, or thespatial wavelength of the undulations, varies as a function of therecorded signal frequency. For reasons of simplic ity it is shown to beconstant in the figures.

A pickup 2 of the type disclosed in the above-cited patents is disposedon the groove undulations 1b to 1e in FIG. 1. This pickup extends overmany groove undulations in the scanning direction, in practice forexample or more undulation projections. The pickup 2 moves from the leftto the right in the plane of the drawing which is equivalent to theactual conditions of a stationary pickup and a carrier moving to theleft.

The pickup 2 is positioned so that its lower surface is below the topsof the projections la-lf when the latter are not stressed.

In the type of system under consideration, the pickup 2 is much lessresilient in a vertical direction than the carrier material so that themovement of the pickup across the undulation projections produces anelastic compression of the carrier material. In order to permit asliding movement of pickup 2 over the groove undulation peaks, itsscanning shown in the drawing has a skid shape so that the pressureacting on this skid over a path of about 1 to 100 wavelength A, (1wavelength distance between the leading edges of two groove undulationprojections) decreases in the direction of movement of the pickuprelative to the carrier. The trailing skid edge, which is to the left inthe drawings, is moreover so designed that the pressure thereat dropsfrom a maximum to zero over a path of travel having a length of no morethan one-half a wavelength (A/2).

In FIG. 1 the groove undulation projections 1b to 1e are compressed bypickup 2 to an increasing extent from the right toward the left due tothe particular shape of the pickup. The displaced portions of thesegroove undulation projections are shown by hatching. If the pickup 2slides over the hill-and-dale recording of FIG. 1, the time curve shownin FIG. 3 results for the force exerted by carrier 1 on the pickup.

FIG. 3 shows that the total force F is greatest when the trailing edgeof the pickup 2 is disposed at the leading edge of an undulationprojection seen in the scanning direction, this being the left-handedge. This force will be identified as F B in the further discussion.Thus, at this point, F,,,, F,;. Such a position is taken up by thepickup in FIG. 1. Thetotal force F,,,, is lowest when the trailing edgeof the pickup, as shown in FIG. 2, lies at the trailing edge of a grooveundulation projection. The difference between this force and F will becalled AF. There thus results for this pickup position the force Tofurther aid understanding of the present invention certain relationshipsfor F and AF will be set forth below.

Under the above-mentioned conditions of constant width transverse to thescanning direction of the groove undulations and of the elastic behaviorof the carrier material, a force component B T is produced by anundulation projection having the length B and which has been compressedby a depth T, which force component directly corresponds in magnitude tothe area of the hatched portion of the groove undulation 1b. The totalforce F F which corresponds to the pickup location of FIG. 1 and whichoriginates from all of the undulations lb to 1e is thus:

un a /A (T2) B k where L is the effective length of the pickup, A thedistance between the leading edges of two successive groove undulationsor an undulation wavelength, and k a constant.

If the pickup 2 moves to the right into the position shown in FIG. 2,the total force decreases by the amount T B k. During this furthermovement of the pickup each of the groove undulation projections 1c to1f is additionally compressed by the amount D B T/L and, since theirnumber is L/A, the force originating from these groove undulationsincreases by the amount If the pulse ratio or duty factor, B/A isrepresented by i, this results in AF=TA-i(li)'k and F =(TL/2 )'i-k FIG.3 shows the curve of the force acting on pickup 2 and originating fromcarrier 1 in the course of the scanning process. Here the maximacorrespond to the pickup position of FIG. 1 and the minima to that ofFIG. 2.

According to the above-derived relationships for F, and AF these twovalues are dependent on the pulse ratio i. F B is directly and linearlyproportional to i. The function AF(i) is shown in FIG. 4.

In the'region i AF is always more than percent of its maximum value andcan thus be considered constant to a first approximation. Outside ofthese preferred limits given for i, AF rapidly drops toward zero, thesignal to noise ratio correspondingly deteriorates in this range withdecreasing AF.

For the simultaneous recording of a second, more slowly varying,information signal, the pulse ratio is correspondingly changed and thusbecomes directly proportional to F The course of F during scanning overa distance s thus results from the superposition of the path of F andthe AF fluctuations representing the frequency modulated recording.

Since F and AF represent separate sources of information, they must beseparable. They must thus lie far enough apart in frequency that theycan be separated with frequency selective filters. The smallestfrequency difference between the two is with respect to the upperfrequency limit of the second signal, which is one-half the lowestfrequency occurring during the frequency modulation of the first signal.The latter frequency is represented by the greatest value of the lengthA occurring in the hill-and-dale recording. As already mentioned, AFincreases proportionally to A according to the equation:

AF=TA-i(l i)-k. Since the signal derived from AF is to remain asconstant in amplitude as possible, however, it can be corrected duringits electrical amplification by the factor NA f/v, where f is therespective frequency of the AF signal and v is the linear speed of thepickup 2 relative to the carrier 1.

A carrier with hill-and-dale recording according to the presentinvention, which simultaneously carries a first frequency modulatedsignal and a second signal S, recorded by a duration or lengthmodulation of the groove undulation projections is shown in FIG. 5a. Thefrequency values of the first signal are represented by the wavelengthsA1, A2, A3, A4, etc., the amplitude of the second signal S, by therespective lengths of the intervals B1, B2, B3 and B4. The amplitudewaveform of the second signal S, which results in the illustratedprojection length modulation is shown in FIG. 5b. The derivation of thelength of the undulations B1 to B4 was based on the particularlyfavorable operating range Ai i 4. This range results for the followingvalue of B, in dependence on A:

S is the peak value of S If the dynamic range of the recording of thesecond signal S2 is limited, eg to 2/5 i 3/ 5, the upper frequency limitof the second signal can be made higher. FIG. 5c shows the variation ofthe force exerted on the pickup by the carrier of FIG. 5a during theplayback process. For the sake of better clarity the dimensions of AF inFIG. 5c, particularly for the fluctuation of force per wavelength, areexaggerated.

The pressure pickup converts this force variation into a correspondinglyvarying electrical voltage. The thus derived electrical signal consists,as shown in FIG. 50, of the rapid voltage fluctuations corresponding tothe frequency modulation (AF) and a total amplitude variation (F (8which corresponds, in the form of an amplitude modulation, to the secondstored signal. These signals can be separated by known electronic means,for example frequency selective filters.

FIG. 6 shows the basic structure of this type of playback device. Amechanical-electrical transducer 11 is placed directly onto a pickup 10.The electrical voltage appearing at the output of transducer 11 travelsthrough a frequency selective filter arrangement 12 to the system 13 inwhich the stored signals are displayed. In the case where a televisionpicture is recorded the system 13 will be a television receiver. In thefilter arrangement 12 the two recorded signals which were picked up bypickup are electrically separated, by techniques which are abundantlywell-known in the art.

As can be seen in FIG. 5a, all groove undulations have the same height.This fact is of great advantage during manufacture of the carrier. Dueto the extremely high information density of the present highdensitystorage system the cutting processes during manufacture of the carrier,which up to now were mechanical processes, must be very precise, whichresults in a relatively low cutting speed. Methods utilizing theelectron beam technique and the laser technique have been proposed tosubstantially increase the cutting speed. The use of known circuitmeasures from the electronic art make it easily possible to produce anelectrical signal from the two sources of information to be stored,which signal corresponds in frequency as well as in its pulse ratio tothe two signals. This electrical signal can then be used, according tothe abovementioned prior proposals, to control an electron or laser beameffecting the recording.

Such circuits are known, for example, from the book Theorie und Technikder Pulsmodulation [Theory and Technique of Pulse Modulation] byl-Ic'ilzler and Holzwarth, published by Springer Verlag, 1957,particularly on pages 17 and 55, and from US. Pats. Nos. 1,917,102,2,171,150 and 2,479,947.

In FIG. 7 is shown as an example an arrangement for forming carriermodulation according to the invention.

FIG. 8 shows the several signals in this arrangement. By a standardfrequency-modulated oscillator the signal S is transformed into a courseof oscillations the frequency of which corresponds to the signal S as isgiven in FIG. 8a. By means of a low threshold circuit 20 this signal istransformed into a course of rectangular pulses the frequency of whichcorresponds to the frequency modulated signal a and the ratio B/A ofpulse duration B to pulse distance A is A, as is shown in FIG. 8b.

This Signal (FIG. 8b) is processed by an integrator 22 of thearrangement shown in FIG. 7 and gives a triangular sequence of pulsesthe amplitude of which is inversely proportional to the frequency of thepulses, as is shown in FIG. 8c. This sequence of triangular pulses feedsa gain controlled amplifier 23, the gain of which is steered either byan automatic gain control or a volume control in dependence on thesignal 8,, in such a way that the amplitude of the triangular pulsesremains constant.

The result of this operation is shown in FIG. 8d. This sequency oftriangular pulses of constant amplitude but of a frequency correspondingto the frequencymodulated signal (FIG. 8a) is applied to a controlledthreshold circuit 24 the height of the threshold of which is derivedfrom the second signal 8,. The result .of this process is shown in FIG.8e.

Now the signal is amplified by an amplifier 25 (FIG. 7) and clipped bythe voltage limiter 26. The result is the signal shown in FIG. 8f. Ifthe signal S should be zero, by the arrangement is produced arectangular pulsetrain the frequency of which corresponds to themodulating signal shown in FIG. 8a, and the ratio of pulse duration topulse distance is again 1%.

But if the threshold differs from zero, the ratio of pulse duration topulse distance corresponds to the value of the threshold andcorrespondingly to the signal S The frequency of the train of pulses(FIG. 8f) corresponds to signal S and the ratio of pulse duration topulse distance corresponds to the signal S The train of pulses accordingto FIG. 8f is the signal wanted for modulation of an electron beam orlaser for producing a record according to the invention.

It is not necessary that the pulses have an exact rectangular wave form.However, the duration of the slopes should be smaller than one-half ofthe duration of the part of the pulse of constant amplitude.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

I claim:

1. In a method for storing signals on a carrier having a deformablesurface portion by which the signals are stored in mechanical form; thedeformable surface portion being arranged along a path over which thereis to be relative movement between the surface portion and, a pressuresensitive pickup which converts changes in the mechanical pressurethereon into electrical signals, the relative movement subjecting thepickup to different pressures as it moves along the path while inengagement with the surface portion, in consequence of which, upon suchrelative movement with the pickup engaging the surface portion andremaining in substantially constant spatial relationship with theundeformed position of the surface portion, the surface portion isdeformed and the pickup produces electrical signals which correspond tothe signals that are stored in mechanical form, the surface portionhaving, in its undeformed state, the form of a series of spatialundulations, each undulation being composed of a to correspond to acharacteristic value of the second signal.

2. A method as defined in claim 1 wherein the ratio between the lengthof a projection and the total length of its associated undulation isgreater than A and less than "$4.

3. A method as defined in claim 1 wherein the highest recorded frequencyof the second signal is lower than the lowest recorded frequency of thefirst signal.

1. In a method for storing signals on a carrier having a deformablesurface portion by which the signals are stored in mechanical form; thedeformable surface portion being arranged along a path over which thereis to be relative movement between the surface portion and a pressuresensitive pickup which converts changes in the mechanical pressurethereon into electrical signals, the relative movement subjecting thepickup to different pressures as it moves along the path while inengagement with the surface portion, in consequence of which, upon suchrelative movement with the pickup engaging the surface portion andremaining in substantially constant spatial relationship with theundeformed position of the surface portion, the surface portion isdeformed and the pickup produces electrical signals which correspond tothe signals that are stored in mechanical form, the surface portionhaving, in its undeformed state, the form of a series of spatialundulations, each undulation being composed of a projection and anadjacent space, the improvement comprising: forming said undulations togive all of said projections a uniform undeformed height above areference plane; recording a first signal by causing the number of saidundulations per unit length of the path to correspond to the frequencyrepresentative of the first signal; and recording a second signal,superimposed on, and independent of, the first signal, by causing theratio of the length of each projection to the total length of itsassociated undulation along the path to correspond to a characteristicvalue of the second signal.
 2. A method as defined in claim 1 whereinthe ratio between the length of a projection and the total length of itsassociated undulation is greater than 1/4 and less than 3/4 .
 3. Amethod as defined in claim 1 wherein the highest recorded frequency ofthe second signal is lower than the lowest recorded frequency of thefirst signal.